Re: [PATCH v6 06/51] x86/sev: Don't override CPU frequency calibration for SNP's Secure TSC

On Thu, 2026-08-06 at 16:35 -0700, Sean Christopherson wrote:

Don't override the kernel's CPU frequency calibration routine when
registering SNP's Secure TSC calibration routine.  SNP (the architecture)
provides zero guarantees that the CPU runs at the same frequency as the
TSC.  The justification for clobbering the CPU routine was:

  Since the difference between CPU base and TSC frequency does not apply
  in this case, the same callback is being used.

but that's simply not true.  E.g. if APERF/MPERF is exposed to the VM, then
the CPU frequency absolutely does matter.

While relying on heuristics and/or the untrusted hypervisor to provide the
CPU frequency isn't ideal, it's at least not outright wrong.

Fixes: 73bbf3b0fbba ("x86/tsc: Init the TSC for Secure TSC guests")
Cc: Nikunj A Dadhania <redacted>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Nikunj A Dadhania <redacted>
Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: David Woodhouse <redacted>

I don't think I care about Sashiko's complaint. Even if we still clamp
it in generic code, I think that's better than having those in the
platform-specific code.